Identification Of Novel Cellobiose-fermenting Yeasts And Their Fermention Characteristics

Cellulose hydrolysis is an essential process of cellulosic ethanol production.Cellobiose is one of the intermediates of cellulose hydrolysis and is a competitive inhibitor of cellulose,which plays a rate-limiting role in the hydrolysis of cellulase.Cellobiose-fermenting yeasts can directly use cellobiose to produce ethanol,which not only can eliminate the inhibition of cellobiose,but also reduce the cost of cellulose hydrolysis,and increase the yield of cellulose ethanol and the efficiency of cellulose utilization.Therefore,cellobiose-fermenting yeasts are important fermenting microorganism for cellulosic ethanol production.The main findings of the study are as follows:1.Isolation and screening of cellobiose-fermenting yeasts.428 yeast strains were isolated from 92 wood samples and 1 tequila sample using YM medium,cellobiose separation medium,xylose separation medium,and xylan separation medium.The yeast strains were tested by Duss methods,and 33 strains were cellobiose-fermenting yeast,the33 strains of cellobiose-fermenting yeast were quickly classified and identified by 26S rDNA D1/D2 sequence analysis,30 of which were known yeasts and distributed in five genera,namely Candida natalensis?2 strains?,Clavispora lusitaniae?3 strains?,Debaryomyces hansenii?11 strains?,Meyerozyma guilliermondii?6 strains?,Wickerhamomyces pijperi?8 strains?.There were 3 strains of novel cellobiose-fermenting yeasts,which namely NYNU 161120^T,NYNU 174173^T,NYNU 17926^T,respectively.2.Identification of novel cellobiose-fermenting yeasts.According to 26S rDNA D1/D2 sequence analysis,ITS sequence analysis and morphology,and physiological and biochemical characteristics,3 strains of novel cellobiose-fermenting yeasts were identified as Clavispora sp.NYNU 161120^T,Clavispora sp.NYNU 174173^T,Scheffersomyces sp.NYNU 17926^T.The type strains are NYNU 161120^T?=CICC 33276^T=CBS 15234^T?,NYNU 174173^T?=CICC 33277^T=CBS 15236^T?,NYNU 17926^T?=CICC 3320^T=CBS15230^T?,respectively.The Mycobank numbers are MF136063,MG255710,MG255714,respectively.3.The fermention characteristics on the novel cellobiose-fermenting yeasts.The fermentation characteristics of cellobiose-fermenting yeasts were studied by glucose fermentation medium and cellobiose fermentation medium.The two strains NYNU161120^T and NYNU 17926^T showed comparatively good fermentation performances through compara.The ethanol yield of the strain NYNU 161120^T in glucose and cellobiose was Y_E/glu=0.59±0.02 g/g,Y_E/cel=0.56±0.02 g/g,separately.The ethanol yield of the strain NYNU 17926^T in glucose and cellobiose was Y_E/glu=0.54±0.02 g/g and Y _E/cel=0.35±0.02 g/g,respectively.